Stabilization of vinyl isocyanates

ABSTRACT

Vinyl-type isocyanates, such as vinyl, isopropenyl, styryl, and vinylphenyl isocyanates, are stabilized by acidified lower aliphatic dialkyl ketals, such as 2,2-dimethoxypropane and butane and 2,2-diethoxypropane. Such ketals inhibit discoloration and/or formation of solids.

Unite distates Patent [191 Hein ert [451, Apr. 17, v1973 [54]STABILIZATION OF VINYL ISOCYANATES [75] Inventor: v Dietrich H, Heinert,Midland, Mich.

[73] Assignee: The Doyv Chemic al Company,

Midland, Mich.

22 Filed: Nov. 1, 1969 21 Appl. No.: 874,981

52 us. or; ..260/453 SP 51 1111. C1 ..C07c 119/04 58 Field of Search..260/453 AL, 453 SP [56} References Cited UNITED STATES PATENTS3,551,468 12/1910 Chadwick ..260/453 3,535,359 10/1970 Chadwick..260/453 OTHER PUBLICATIONS Wagner and- Zook: Syn. Org. Chem., pp.261-262, John Wiley & Sons (1953).

Primary Examiner-Lewis Gotts Assistant Examiner-Dolph l-l. TerrenceAtt0rneyGriswold and Burdick and C. E. Rehberg [5 7 ABSTRACT 9 Claims,No Drawings BACKGROUND OF THE INVENTION This invention relates toadditives for the stabilization of vinyl isocyanates and to the productsthus stabilize d.

Isocyanates are extremely reactive toward water or other materialscontaining active hydrogen and are also very easily oxidized,polymerized and otherwise modified or degraded..The vinyl isocyanatesare much more sensitive to these various degrading influences than arethe ordinary alkyl, alkylene or arylene isocyanates. Accordingly, theproblem of stabilizing the vinyl isocyanates is a particularly difficultone in that many stabilizers that are effective and satisfactory in theordinary isocyanates do not satisfactorily stabilize the vinylisocyanates.

Aliphatic ketals, particularly 2,2-dimethoxypropane (hereinafter DMP)are known to be moisture scavengers and have been used as stabilizers inpolyurethane formulations containing isocyanate groups (U.S. Pat.

No. 3,376,252). They have also been used to remove moisture fromfillers'to be used in making filled polyurethane resins (Application ofK, E. Hinze and L. E.

Peterson, Ser. No. 839,671, filed July 7, I969).

SUMMARY OF THE INVENTION It has now been found that vinyl isocyanatesare stabilized by incorporation therein of (l) 2,2-dimethoxypropane(DMP), 2,2-dimethoxybutane, 2,2-diethoxypropane, 3,3-di-n-butoxypentane,or similar lower dialkyl aliphatic ketals and (2) a catalytic amount ofa strong acid that effectively catalyzes the hydrolysis of DMP.

The preferred ketals are those having the formula -R-C(OR') --R" whereineach of R, R' and R" independently is lower alkyl; i.e., alkyl of one tofour carbon atoms. Most preferred are those ketals containing a total ofnotmore than seven carbon atoms.

The amount of ketal needed for stabilization depends largely on thewater content of the isocyanate, including any water that might bepicked up in handling and storing the material, and should include asuitable safety margin. Theoretically, one mole of ketal should removeone mole of water. While the ketal-water reaction is normallyreversible, and goes only to 92 percent completion at 30C. when reactedin a 1:1 molar ratio in the absence of other materials, I have found,unexpectedly, that they react essentially quantitatively in the presenceof the vinyl isocyanates. Accordingly, a molar ratio of about 1.5:1,based on the actual or expected water content of the isocyanate,ordinarily provides adequate protection. When normal precautions toexclude water are taken, the water content will usually be of the orderof 0.1%. For such material, about 0.3 0.5 percent by wt., based on vinylisocyanate, is usually quite adequate. Since the ketals are inexpensiveand readily available, and their presence in the isocyanate isordinarily unobjectionable, larger amounts, up to 5 percent or more, maybe used without raising any problems, thus providing additionalprotection in case of unforeseen contamination with water.

The acid catalyst to be used in the practice of the invention may be anyacid that catalyzes the reaction of the vinyl isocyanate with waterwithout itself having a deleterious effect on the isocyanate. Such acidsinclude the hydrogen halides (HCI, HBr or HF), BF and the strong organicacids, such as trichloroacetic acid, trifluoroacetic acid, formic acid,monochloroacetic acid, difluoroacetic acid, p-toluene sulfonic acid,methane sulfonic acid, pyridinium hydrochloride, etc. Such catalystsshould, of course, be essentially .anhydrous. Organic acid halides,e.g., acetyl chloride, chloroacetyl chloride, trifluoroacetyl chloride,ptoluene sulfonyi chloride and the like are also effective catalysts andare included in the term acid catalyst as used herein.

The amount of catalyst required depends on the particular materials usedbut in any case is a small catalytic amount. When using the preferredcatalysts, trifluoroacetic acid, I-ICl or acetyl .chloride, with DMP,about 0.005 to 0.1 moles of catalyst per literof isocyanate is suitable,the preferred concentration being about 0.02 to 0.06 moles per liter.

SPECIFIC EMBODIMENTS OF THE ll'tlVENTION The following examplesillustrate the practice of the,

invention.

EXAMPLE 1 In the production of vinyl isocyanate by the method disclosedin my US. Pat. No. 3,470,228, the reactor effluent, after passingthrough stripper condensers at room temperature and at -46C. to removeuncracked trivinyl isocyanurate and other materials of low volatility,was passed into a trap in a bath of liquid N (-l96 C.). This trap wasprecharged with 10 g. of mdinitrobenzene, 47.8 ml. of DMP and 2.22 ml.of trifluoroacetic acid. This trap was connected in turn, through amanifold, to a second trap, similarly cooled, charged with 10 g. ofm-dinitrobenzene. A third and final trap connected to the manifold wascharged with 4.8 ml. of DMP and 0.3 ml. of trifluoroacetic acid. Thistrap was initially isolated from the manifold bya closed valve. Thefunction of the dinit'robenzene in these traps was to inhibitpolymerization of the vinyl isocyanate through the vinyl group, thoughit was observed in preliminary runs that this inhibitor alone did notcompletely prevent polymerization of the crude product. Since water isknown to initiate polymerization of the material through the isocyanategroup, the

- DMP and acid catalyst were used to prevent such polymerization. It hasbeen found that even the traces of moisture absorbed on the surfaces ofthe equipment and containers are sufficient to cause gradualpolymerization of even highly purified vinyl isocyanate.

thus maintaining a pressure of about 1 mm. therein.

The cooling bath was then removed from the second cold trap, thuscausing the trap to become warm and distilling volatile materials fromthe second to the first trap. The cooling bath was then removed from thelatter and the contents allowed to warm gradually, the

pressure then also' rising gradually. At atmospheric pressure the systemwas vented to the atmosphere. At about l5C., a reaction began betweenthe vinyl isoa 12 inch Vig'reux column it still remained unchanged.

When the above experiment was repeated with omission of the DMP andtrifluoroacetic acid, the product became turbid after a day or two andwithin one month over 20% of it had polymerized. When. thenonpolymerized portion was distilled, the distillate polymerized almostcompletely within one day.

EXAMPLE 2 ble after 3 hr. at room temperature.

in a control experiment identical with that above except that the DMPand trifluoroacetic acid were omitted, analyses 5 min. and 30 min. afterthe addition of the water showed 0.1. and 0.05 percent water,respectively and distillation yielded a distillate that became turbidwithin 30 min. at room temperature.

EXAMPLE 3 To determine the effectiveness of DMP in inactivating largeramounts of water and to compare different acid catalysts, three parallelexperiments were run.

Into each of three flasks fitted with stirrers and reflux condensers wasplaced 50 ml. of pure vinyl isocyanate. Into the first and second flaskswas also put 5 ml. of DMP. Into the first was also put 0.25 ml. oftrifluoroacetic acid. Into the second was put 90 ml. (STP) of gaseousanhydrous HCl. Then, into each flask was put 0.5 ml. of water (1 percentby ml). The first and second flasks became slightly warm, due to thereaction of the isocyanate with the methanolreleased from the DMP and asmall, fluffy precipitate formed in the firstQThe second remained clearand colorless. A massive precipitate in thethird flask solidified to thepoint that the stirrer was stalled.

After 4 days the material in the three flasks was distilled to recoverany remaining vinyl isocyanate and to determine the stability of thedistillate thus obtained. Results are shown in the following table.

Flask Monomer No. Recovered, 1: Stability of Distillate l 86 i Slightturbidity after 1 day Clear and colorless after 1 month polymerizedimmediately and completely I EXAMPLE 4 Two glass bottles were oven-driedat l'l0C. One of the bottles and a metal can were then soaked 30 min. ina solution of 50 ml. of DMP and 2.5 ml. I of. trifluoroacetic acid in 1liter of trichlo'roethylene and then drained. The three containers, allprotected from atmospheric moisture in a dry-box, were then filled withpure, unstabilized vinyl isocyanate and tightly closed. After storagefor 40 days at room temperature, the three samples were distilledtodetermine extent of polymerization and stability of the distillate.Results are shown in the following table.

Stability Monomer Container Recovered, of Distillate Ovemdried glass94.0 Turbid after 2 hrs. Treated glass 97.6 Clear after 24 hrs. Treatedmetal can 97.8 Clear after 24 hrs.

Results similar to those described above are obtained with other vinylisocyanates, such as isopropenyl, styryl or vinylphenyl isocyanate, andwith other aliphatic dimethyl ketals, such as 2,2-dimethoxybutane or3,3- dimethoxypentane.

Iclaim:

l. The process of stabilizing vinyl isocyanate, isopropenyl isocyanate,styryl, isocyanate or vinylphenyl isocyanate comprising maintainingtherein a stabilizing amount of ketal of the formula R-C(OR'),-R"wherein R, R and R" are lower alkyl groups and a catalytic amount of asubstantially anhydrous .acid catalyst that catalyzes the reaction ofwater with said ketal and is free of deleterious effect on theisocyanate.

2. The process of claim 1 wherein the isocyanate is vinyl isocyanate.

3. The process of claim 1 wherein the ketal is 2,2- dimethoxypropane. v

4. The process of claim 1 wherein the catalyst is trifluoroacetic acid,acetyl chloride or hydrogen chloride.

5. Vinyl isocyanate, isopropenyl isocyanate, styryl isocyanate orvinylphenyl isocyanate containing a stabilizing amount of a ketal of theformula R-C(OR" -R" wherein R, R and. R" are lower alkyl groups and acatalytic amount of a substantially anhydrous acid catalyst that iseffective to catalyze the reaction of water with said ketal and is freeof deleterious effect on the isocyanate. 1

6. The composition of claim 5 wherein the isocyanate is vinylisocyanate. 1

7. The composition of claim 5 wherein the ketal is 2,2-dimethoxypropane.1

8. The composition of claim 5 wherein the catalyst is trifluoroaceticacid, acetyl chloride or. hydrogen chloride. 'I i 9. The composition ofclaim -5 whereinthe isocyanate is vinyl isocyanate, the ketal is2,2-dimethokypropane and the catalyst is trifluoroacetic acid.

a s e m a

2. The process of claim 1 wherein the isocyanate is vinyl isocyanate. 3.The process of claim 1 wherein the ketal is 2,2-dimethoxypropane.
 4. Theprocess of claim 1 wherein the catalyst is trifluoroacetic acid, acetylchloride or hydrogen chloride.
 5. Vinyl isocyanate, isopropenylisocyanate, styryl isocyanate or vinylphenyl isocyanate containing astabilizing amount of a ketal of the formula R-C(OR'')2-R'''' wherein R,R'' and R'''' are lower alkyl groups and a catalytic amount of asubstantially anhydrous acid catalyst that is effective to catalyze thereaction of water with said ketal and is free of deleterious effect onthe isocyanate.
 6. The composition of claim 5 wherein the isocyanate isvinyl isocyanate.
 7. The composition of claim 5 wherein the ketal is2,2-dimethoxypropane.
 8. The composition of claim 5 wherein the catalystis trifluoroacetic acid, acetyl chloride or hydrogen chloride.
 9. Thecomposition of claim 5 wherein the isocyanate is vinyl isocyanate, theketal is 2,2-dimethoxypropane and the catalyst is trifluoroacetic acid.